Posterior Hip Dislocation Anatomy
No, in a posterior hip dislocation, the acetabulum (hip socket) is NOT posterior to the femoral head—rather, the femoral head is displaced posteriorly out of the acetabulum. The acetabulum remains in its normal anatomical position while the femoral head moves backward and upward, typically coming to rest posterior and superior to the acetabular socket.
Understanding the Anatomical Relationship
In a posterior hip dislocation, which accounts for approximately 83% of all traumatic hip dislocations 1:
- The femoral head displaces posteriorly out of its normal position within the acetabulum
- The acetabulum stays fixed in its anatomical location as part of the pelvis
- The femoral head typically comes to rest posterior and superior to where it should be
Clinical Context from Examination Maneuvers
The Barlow test for developmental dysplasia provides insight into this relationship: the examiner attempts to "gently adduct the thigh and dislocate the femoral head posteriorly" 2. This confirms that posterior dislocation involves the femoral head moving backward relative to the fixed acetabulum, not the acetabulum moving behind the femoral head.
Associated Injuries
Posterior hip dislocations frequently occur with:
- Posterior acetabular wall fractures (81.25% of cases) 1
- Femoral head fractures 3
- The posterior acetabular rim may impact against the femoral head, creating osteochondral impaction fractures 4
Common Pitfall
Do not confuse the direction of dislocation with the relative position of structures. When we say "posterior dislocation," we're describing where the femoral head has moved (posteriorly), not suggesting the acetabulum has moved behind the femoral head. The acetabulum is a fixed bony socket that cannot spontaneously relocate—only the femoral head dislocates.